Python Pandas：从现有列创建日期数据框

Question

I have a pandas dataframe with a column for years and one for months. How can I create a new date column based on these two (I can assume day = 15).

I tried the following:

import pandas as pd
import numpy as np
import datetime  

df = pd.DataFrame()
df['year'] = np.arange(2000,2010)

df['mydate']= datetime.date( df['year'].apply(lambda x: int(x)) , 1 , 1)

but I get this error message:

 df['mydate']= datetime.date( df['year'].apply(lambda x: int(x)) , 1 , 1) File "C:\\Anaconda\\lib\\site-packages\\pandas\\core\\series.py", 

line 77, in wrapper "cannot convert the series to {0}".format(str(converter))) TypeError: cannot convert the series to

which I don't understand because I explictly convert x to int.

Thanks!

Answer 1

You can build another column based on the existing columns by using df.apply(fnc, axis=1) .

In your case this becomes:

df = pd.DataFrame()
df['year'] = np.arange(2000,2010)
df['month'] = 6

df['date_time']= df.apply(lambda row :
                          datetime.date(row.year,row.month,15), 
                          axis=1)